Field of the Invention
The invention relates to a method for creating time-resolved magnetic resonance (MR) images of an examination subject and a magnetic resonance apparatus for this. The invention relates, in particular, to methods and MR apparatuses that enable time-resolved imaging of flow rates.
Description of the Prior Art
The local and temporal resolved imaging of flow rates has multiple applications, such as the examination of the heart, for example. A multi-dimensional phase-contrast MR imaging can be used for measuring flow rates. For a time-resolved determination of the speed, data must be acquired for numerous different speed encodings for numerous time segments. In addition to a data acquisition with a sequence having flow compensation, at least one other data acquisition is made, in which the speed encoding gradients are applied such that speeds along a certain spatial direction are recorded, for example. The large number of dimensions of the data space (temporal resolution, two to three spatial directions, speed encoding in one or more spatial directions) results in long data acquisition times.
To reduce the data acquisition times, parallel imaging methods and methods with underscanning have been developed into valuable and promising methods. The use of conventional SENSE (“Sensitivity Encoding”) or GRAPPA (“Generalized Autocalibrating Partially Parallel Acquisition”) methods can result in the problem that with an imaging with speed encoding, the acceleration factors are not particularly large, and/or a contrast/noise relationship is strongly deteriorated. Daniel Kim et al., “Accelerated Phase-Contrast Cine MRI using k-t SPARSE-SENSE,” Magn Reson Med. 2012 Apr.; 67(4), Pages 1054-1064, describes a method for phase-contrast MR imaging, which likewise combines a parallel data recording with numerous receivers and underscanning. DE 10 2011 081 411.6 describes a scanning pattern for an MR imaging, in which the MR images are calculated using iterative reconstruction methods.